The present invention relates to a recycling automatic document feeder (RADF) for a copier which feeds a stack of documents one by one from a document table to an exposing position, returns the document from the exposing position to the top of the document stack after imagewise exposure, and refeeds such documents one by one to the exposing position.
Various kinds of copiers, printers and facsimile machines are extensively used as an image forming apparatus for forming images of documents. With this kind of image forming apparatus such as a copier, a RADF is available as means for automatically feeding documents one by one to a glass platen so as to save time and labor. A RADF has a belt for feeding documents stacked on a document table one by one, the lowermost document being first, to a glass platen of the copier body via an inlet. After the document has been scanned for exposure, the belt returns it to the top of the document stack on the table via an outlet. Specifically, the documents are repetitively routed through a circulation path made up of a feed path and a return path in order of page and by a number of times associated with the desired number of copies. To preserve the copying order of the stack of documents, it is necessary that the document driven out from the outlet after imgewise exposure be at least partly laid on the uppermost document. Also, to refeed the circulated document to the feed path, it is necessary that the document driven out from the outlet be at least partly laid on the belt. More specifically, the distance l.sub.1 between the outlet and the inlet, the distance l.sub.2 between the outlet and the rear end of the belt, and the length L of the document as measured in an intended direction of document feed have to be related to one other, as follows: EQU l.sub.1 /2&lt;L.ltoreq.l.sub.1 and L&gt;l.sub.2
The above relationships cannot be satisfied without imposing substantial limitations on the length of the document as measured in the intended direction document feed which is usable with the RADF.
A RADF whose outlet, for example, is variable in position in matching relation to the length of documents as measured in the intended direction of document feed has been proposed to eliminate the above limitations. Specifically, such a RADF shifts the outlet by using a telescopic discharge guide or a foldable discharge belt. This implementation, however, does not allow the outlet to move beyond a certain limited range and needs a complicated structure. A RADF capable of shifting the outlet over a substantial range by a relatively simple construction is disclosed in, for example, Japanese Patent Laid-Open Publication (Kokai) No. 143125/1988. However, the RADF proposed in this Laid-Open Publication cannot operate satisfactorily with a broad range of document lengths and, when its return path is jammed by a document, needs troublesome operations for the removal of the jamming document.